Information recording medium, information recording method and information recording apparatus

ABSTRACT

A recording medium having a dummy signal area on at least one side of a recording area is used and information is recorded with a dummy signal added to at least one of the leading and trailing sides in the recorded information signal. The user data area remains unaffected by repeated overwriting so that recorded user data is reproduced correctly. In particular, the wave form distortion caused by fluidization of a recording film remains at the dummy signal area and does not affect the user data area, so that the reproduction of the target information (user data) is assured.

FIELD OF THE INVENTION

[0001] The present invention relates to an information recording medium,an information recording method and an information recording apparatuswhich are capable of recording such information in real time by means ofrecording beams, for example, laser beams as digital informationincluding pulse-frequency modulated analog signals of projected imagesand voice, data in electronic computers, facsimile signals and digitalaudio signals. More particularly, the present invention relates to adisk shaped recording medium using an erasable, phase-change typeoptical recording film.

BACKGROUND OF THE INVENTION

[0002] Conventional phase-change type optical disks have a recordingfilm capable of fast erasure by crystallization that is materializedwithin a time substantially equal to the time required for a recordinglaser beam to pass on a point on a disk, for example. The conventionalmethod of recording and erasing information to and from such an erasablerecording film is to change the power of the laser beam between twolevels higher than the reading power levels, these levels are a highpower level and an intermediate power level. The advantage of thismethod is that the so-called overwriting (replacing old information withnew without prior erasing) is possible. When such overwriting isrepeated a plurality of times, however, the laser beam irradiates therecording film repeatedly in accordance with the recording informationsignal. This results in a high probability of allowing VFO recordingmarks to be repeatedly written to the same place in an area close to apreformat section in particular, and therefore variations in filmthickness tend to occur locally because of recording film fluidization.

[0003] According to Japanese Unexamined Patent Publication No.150725/1991, a method that avoids the recording film from beingrepeatedly written at the same place involves shifting the data writestart position each time data is written or at appropriate times whenold data is overwritten, whereby mark-forming positions are properlydistributed. Thus the overwriting cyclability of the optical disk areimproved.

SUMMARY OF THE INVENTION

[0004] Even when information is recorded on the phase-change typeoptical disk as in the prior art, the fluidization of the overallrecording film inevitably occurs as overwriting is repeated a pluralityof times because the temperature distribution in the laser beam isasymmetrical. Consequently, a change in the thickness of the recordingfilm is brought about in that the film becomes thick on one side andthin on the other side (the initial or terminal end portion of arecording area taken from the perspective of the direction of recording)or the film becomes thick at the center portion of the recording areaand thin at the starting and ending areas, so that the distortion of thereproducing signal waveform also occurs. The latter type of thicknesschange is more difficult to stop. Therefore, there arises a problem ofmaking the area having the waveform distortion expand as the number ofoverwriting times increases. In the case of an erasable digital videodisk, moreover, mark edge recording may be used with both edges of arecording mark provided with information for the purpose of increasingdensity. When such a mark edge recording system is employed,deterioration due to fluidization is further evident because a long markis repeatedly recorded.

[0005] An object of the present invention intended to solve theforegoing problems in the prior art is to provide an informationrecording medium, an information recording method and an informationrecording apparatus that ensure reproduced F signals properlycorresponding to recorded information signals.

[0006] According to the present invention, a recording medium capable ofrecording or overwriting information with a laser beam is provided. Therecording medium has a preformatted area in which information such as atrack address has been formed with pits or with recording marksresulting from a phase change. In addition to the preformatted area, agap area, a recordable area such as a VFO/SYNC area and a user data areaare reserved. Moreover, a dummy area is provided on at least one of thesides before and after the recording area. A part of the VFO area can beused instead of the front dummy area, by making the VFO area long.Further, a buffer area to allow for a margin for the rotational jitterof a motor is located just after the dummy area. In this case, one ofthe objectives for the provision of the dummy area is to preventinformation actually read from the user data area from being damagedeven though repeated overwriting causes the fluidization of therecording film. Such damage is prevented because the distortion of areproduced signal waveform is confined to the VFO/SYNC area and/or thedummy area. Further, the dummy area is preferably set to be longer thanthe maximum shift width of a position where the writing of a recordedinformation signal is started. Further, it is preferable to add a pitarray (data area postamble) depending in accordance with applicablestandards before this dummy area to avoid the mark and the space frombeing inverted.

[0007] According to the invention, recording is made by adding a dummysignal to at least the front or rear side of a target (recorded) signalsuch as VFO, SYNC and user data. It is preferable to add the dummysignal to the rear side (the trailing side with respect to the directionof recording) when a dummy signal is added to only one side of thetarget signal. In this case, the dummy signal is chiefly recorded in thedummy area.

[0008] Further, according to the invention, the fluidization of therecording film resulting from repeated overwriting can be moderated bysetting the average energy of the laser beam during dummy signalrecording to be lower than that during the target information signalrecording. Consequently, the distortion of the reproduced signalwaveform due to the fluidization slightly occurs in the dummy area wherethe dummy signal is recorded and in part of the buffer area. However,the recording area where the target signal is recorded remainsunaffected by the fluidization to ensure that a reproduced signalcorrectly corresponding to the target signal is obtained. Collectively,the sum of the dummy area and the buffer area can be called a bufferarea.

[0009] For the recording of the dummy signal, the average energy thereofmay be lowered, for example, by adjusting the duty ratio of asingle-frequency signal. In a mark edge recording system, the duty ratioof the dummy signal may be set to not greater than 50% because theaverage duty ratio is about 50%. The duty ratio of at least a part ofthe dummy signal is preferably in a range of at least 10% to about 40%,and more preferably in a range of at least 20% to about 30%. Moreover,the average energy of the laser beam during the recording of the dummysignal may be decreased stepwise or linearly by adjusting the duty ratioof the dummy signal stepwise or linearly; or otherwise the recordingpower may be varied. It is more preferred to vary the duty ratio of thedummy signal than to vary the recording power in order to simplify theapparatus. The dummy signal may be added to either the front or rearside of the recording information signal, that is mainly VFO, SYNC, anduser data, depending on the recording media characteristics. In thepreferred case of adding the dummy signal to only one side,.the dummysignal is added to only the rear side of the recorded information signalrather than the front side where the VFO has a function of the dummysignal.

[0010] The distortion level of the reproduced signal waveform can alsobe lowered by shifting the start position of writing the recordedinformation signal to effect overwriting. In this case, the maximumshift width is preferably set to be shorter than the dummy signal thatis added; particularly, it is preferably set to be approximately{fraction (1/20)} to ½ of the length of the recorded dummy signal.

[0011] Also according to the present invention the recording mediumstores thereon information concerning the pattern of the dummy signalthat is used, for example the duty cycle of the dummy signal. Forexample, it is preferred that such information be recorded in thecontrol data area of the recording medium.

[0012] Recording films utilizing a phase change such as recording filmsof a Ge—Sb—Te system and a Ag—In—Sb—Te system may be used according tothe present invention. The use of a recording film containing ahigh-melting point material such as Cr—Te and Ag—Te whose melting pointis higher than that of the main component material and a recordingmedium with an Si/metal double reflective layer is preferred because therecording film thickness is further restrained from varying because offluidization.

[0013] Still further, according to the present invention, information isrecorded by an information recording apparatus including: a laser beamsource, an optical system, automatic focusing (AF) means, trackingmeans, reproduced signal detection means, means to read information in acontrol data area, a recording medium on which information on a patternof a dummy signal to be added to at least one of the leading or trailingsides of a recorded information signal is recorded beforehand, means forrotating or moving the recording medium, means for condensing laserbeams from the laser beam source on the recording medium, signalmodulating means for converting a signal to be recorded into amodulation code, means for adding the dummy signal as set forth herein,recording waveform generation means for generating a recording waveformcorresponding to the recording code with the dummy signal added,recording start position control means for shifting a recording startposition at random (preferably wherein the maximum shift width of therecording start position, for example, expressed in a unit of Bytes isshorter than the length of the dummy signal expressed in a unit ofBytes), laser driving means for driving the laser beam source inaccordance with the recording waveform, means for converting theintensity change of the laser beam reflected from the recording mediuminto an electrical signal, means for amplifying the reproducedelectrical signal, binary conversion means for converting the electricalsignal into a binary waveform, means for deleting the dummy signal, andmeans for decoding the binary signal to make the decoded signal aninformation signal (user data).

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a partial sectional view of a disk embodying the presentinvention.

[0015]FIG. 2 is a diagram of an exemplary sector format according to anembodiment of the invention.

[0016]FIG. 3 is a block diagram of an information recording apparatusaccording to an embodiment of the invention.

[0017]FIG. 4 is a flow chart showing the steps followed in generatingthe dummy data by reading information on the dummy data pattern from adisk after the disk is inserted in the apparatus of the invention;

[0018]FIG. 5 is a diagram of an example of the data area postamble andthe dummy data according to the invention; and

[0019]FIG. 6(a) and 6(b) are diagrams of examples of the dummy datapattern according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] A detailed description will subsequently be given of thepreferred embodiments of the present invention.

[0021] The recording film for use in the present invention is preferablya crystal-amorphous phase-change optical recording film capable of fastcrystallization, a recording film utilizing an amorphous-amorphouschange, a crystal-crystal phase-change (e.g. a change in the crystalsystem and particle size) recording film or a magneto-optic recordingfilm. However, any other recording film which has a tendency to havewaveform distortion at the beginning and/or the end of a recording areamay also be used.

[0022] In addition to the preformatted area and a gap area, a recordingarea such as the VFO/SYNC area and the user data area capable ofrecording information are provided. Moreover, the dummy area is providedon at least one of the leading or trailing sides located respectivelybefore and after the recording area, and this dummy area serves toprevent information actually read from the data area from being damagedeven though repeated overwriting causes the fluidization of therecording film. The damage is prevented because the distortion of theregenerative signal waveform resulting from the fluidization thereof isconfined to the VFO area, the dummy signal and/or the buffer area.

[0023] A description will subsequently be given of the functions in acase where a recording medium is used in which forward fluidization (therecording film is fluidized in the same direction as the direction inwhich the laser beam proceeds along the surface of the disk) is causedtherein by a plurality of overwritings. The sector format of therecording medium used herein includes the preformatted area, the gaparea, the front dummy area, the recording data area, the rear dummy areaand the buffer area arranged in this order. The recording data area isformed with the VFO/SYNC area and the user data area. At this time, theshift width at the recording start position is made shorter than thelength of the dummy area to ensure that the recorded information signalis correctly reproduced. When overwriting is repeated a plurality oftimes on the recording medium, fluidization occurs and the fluidizedportion of the recording film moves from the beginning or leading sideto the trailing or ending side of the recording area. Therefore, thereproduced signal level varies.

[0024] In this recording medium, a reflectance first decreases, thenincreases as the recording film becomes thinner and increases as itbecomes thicker. In other words, the reflectance first decreases thenincreases on the leading side where the recording film becomes thin,whereas it increases on the trailing side where the recording filmbecomes thick. Therefore, the distortion of the reproduced signalwaveform occurs on the leading and trailing sides of the recording area,thus causing errors. However, the error generation resulting fromrepeated overwriting can be eased by adding the dummy signal to at leastone of the leading or trailing sides respectively before or after atarget information signal such as the VFO/SYNC and data signal recordingarea and by making the average energy of the dummy signal lower thanthat of the recorded user data signal. At the time of the reproductionthen, only the reproduced signal waveform corresponding to the user datasignal is reproduced, whereby the user data recording area remainsunaffected by the fluidization even though the reproduced waveformdistortion in the dummy signal area and/or that of the buffer area occurto ensure that the user data signal is reproduced correctly. Further, nogreat distortion is caused in the reproduced signal waveform of therecorded user data signal even if the number of overwritings increases.

[0025] In this case, the average energy of the laser beam during thedummy signal recording may be lowered by, for example, recording thedummy signal with a single-frequency signal and decreasing the dutyratio of the signal. In the mark edge recording system, the duty ratioof the dummy signal may be set to not greater than 50% because theaverage duty ratio of the user data is about 50%. In the case of a diskcausing the forward fluidization, the duty ratio of the dummy signalshould preferably be decreased further to as low as 25%. Moreover, theaverage energy of the laser beam during the dummy signal recording maybe decreased stepwise or consecutively by adjusting the duty ratio ofthe dummy signal stepwise or linearly; or otherwise, the laser powerlevel may be varied instead of the duty ratio.

[0026] Although the average laser beam energy can be decreased byvarying the pulse width of the recording waveform and/or the power thatis used, it is preferred to vary the duty ratio of the dummy signalbecause the apparatus is simplified. The dummy signal may be added toeither the front (leading) or rear (trailing) side or both of therecorded information signal as occasion demands. In this case, the dummysignal may be added to only the rear (trailing) side of the recordedinformation signal rather than the front side thereof where the VFOsignal has a similar function as that of the dummy data signal.

[0027] Although the invention is disclosed with respect to a disk mediumembodiment, any other recording medium in the form of not only a diskbut also a card and the like is applicable to the present invention.

[0028]FIG. 1 is a partial sectional view of a disk used according to apreferred embodiment of the invention. First, a ZnS—SiO₂ dielectriclayer 2 about 125 nm thick is formed by magnetron sputtering on apolycarbonate substrate 1 for a continuous tracking servo, the substrate1 having a diameter of 5 inches and a thickness of 0.6 mm. Subsequently,a recording film 3 of Cr₅Ge₂₀Sb₂₀Te₅₅ is formed to about 30 nm thicknesson the ZnS—SiO₂ dielectric layer 2 and additionally a ZnS—SiO₂dielectric layer 4 about 20 nm thick is formed on the recording film 3.Further, an Si layer 5 is formed to about 100 nm thickness on thedielectric layer 4 and then an Al—Ti—alloy reflective layer 6 about 100nm thick is formed on the Si layer 5.

[0029] The formation of these film layers is carried out successively byone and the same sputtering apparatus. Further, anultraviolet-light-hardening resin layer 7 is applied onto the alloyreflective layer 6 and then a hot-melt adhesive layer 8 is used toadhere a protective layer 9 securely onto theultraviolet-light-hardening resin layer 7. In this case, it is possibleto obtain a bonded disk having a recording capacity twice as large asthat of the above bonded laminate by bonding, in place of the protectiveplate 9, another disk as a combination ranging from the polycarbonatesubstrate 1 up to the ultraviolet-hardening resin protective layer 7.

[0030]FIG. 2 shows an example of a sector format of the substrate usedaccording to the preferred embodiment of the invention. The sectorformat includes a preformatted area 10 where information such as sectorand track addresses are formed as uneven pits. In addition to thepreformatted area 10 which is a read-only area, a gap area 11 and arecording area 14 (group section) such as a VFO/SYNC area 12 and a userdata area 13 capable of being recorded (including overwriting) withinformation are provided.

[0031] According to this embodiment of the invention, moreover, dummyareas 15, 16 are provided at the beginning and the end in the recordingarea, respectively. Further, a buffer area 17 providing a margin for arotational jitter is also provided behind the dummy area 16 whichfollows the recording area. The dummy areas 15, 16 serve to preventinformation that is read from the user data area 13 from being damagedeven though repeated overwriting causes the fluidization of therecording film. This damage is prevented because the distortion of areproduced signal waveform resulting from the fluidization thereof isconfined to only the front-side dummy area 15 before the VFO/SYNC areaand further because the distortion of the reproduced signal waveformresulting therefrom is confine to the rear-side dummy area 16 behind theuser data area. In this case, the dummy areas 15, 16 are set to belonger than the maximum shift width at a position where the writing of arecording signal is started, and the rear-side dummy area 16 whoserecording film thickness varies greatly due to the fluidization is setto be longer than the front-side dummy area 15. According to recordingmedia characteristics, such a dummy area for restraining the effect offluidization may be provided on either front or rear side, andpreferably on the rear side if it is to be provided on only the oneside.

[0032] In this embodiment, a dummy signal is added, as an example, toboth sides of a recorded information signal by a time length of 500 Tw(1 Tw: 90 ns, wherein Tw represents a reproduced signal detection windowwidth). Further, in this embodiment, a recording start position isshifted at random within a range of 360 Tw. In this case, the dummysignal is mainly recorded in the dummy area. In order to moderate thefluidization of the recording film resulting from repeated overwriting,moreover, the average energy of the dummy signal is set to be lower thanthat of the user data signal; in other words, affected area by thefluidization is made to increase gradually.

[0033] In practice, a single-frequency (recording pulse period: 10 Tw)signal is used for the dummy signal and the duty ratio of the signal isset low. In the case of a mark edge recording method, the duty ratiobecomes substantially equal to 50% in terms of the average energy whenthe recording is made at the single frequency. Consequently, the dutyratio of the dummy signal is preferably not greater than 50%.

[0034] Since the recording film is fluidized in the same direction asthe direction of the laser beam (forward fluidization) due to repeatedoverwriting on the disk of this embodiment according to the invention,the duty ratio is set as low as 30%. The effect of adding the dummysignal was noticeable when the duty ratio was at least 10% and up to andincluding 40%. The effect was especially pronounced when the duty ratiowas in the range of at least 20% up to and including 30%, whereby theeffect of fluidization of the recording film was significantly easedwith the effect of enlarging the recording power margin. Moreover, theaverage energy of the laser beam during dummy signal recording, may,according to various conditions, be decreased stepwise or linearly. Inthis embodiment, the recording laser pulse corresponding to a recordingmark was divided into a plurality of pulses by a recording waveformgenerator. Thus the laser pulse duty was less than 50% even for therecording of the user data.

[0035] The reproduced signal waveform distortion due to fluidization hasbeen reduced by randomly shifting the write start position of therecorded information signal by an amount approximately equal to{fraction (1/20)} to ½ of the dummy signal area.

[0036] Information on the pattern of the dummy signal (e.g., informationon a single-frequency pattern in which the average recording mark lengthrecorded by the dummy signal becomes shorter than the average spacelength between the recording marks, etc.) is recorded with pitsbeforehand in the control data area of the disk in this preferredembodiment of the invention; thus recording is made according to thisinformation.

[0037] Compared to a Ge—Sb—Te or A—In—Sb—Te recording film to which nohigh-melting point material such as Cr—Te has been added, a recordingfilm containing a high-melting point material such as Cr—Te and Ag—Te,for example, Ag₂Te is preferred because the recording power margin formoderating the fluidization is attainable to a great extent, though theuse of the recording waveform with the dummy signal added thereto hasthe effect of suppressing the effect of fluidization.

[0038]FIG. 3 is an exemplary block diagram of a record playback systemin a record playback apparatus embodying the present invention. Beforethe recording, dummy data is generated according to information storedin the control data concerning the dummy data pattern, then the dummydata is stored in a memory 41. At the time of recording, the primarysignal to be recorded (user data) is fed into a modulator 18 in which itis converted into a modulation code. The dummy data generated and storedin the dummy data memory 41 is read out through the dummy data patternreading circuit 42 and added to the user data with an adder 43. Further,VFO and SYNC signals are added with an adder 44. Also, the pulse signalfrom the adder is passed through a recording start position controller20 for shifting a recording start position of the recording signal atrandom. Then a recording waveform corresponding to a target recordingcode is formed by a recording waveform generator 19 before being outputas recording pulse signals. A laser driver 21 modulates the drivingcurrent of a semiconductor laser 22. Further, a disk 24 is irradiatedwith a condensed laser beam via an optical system in an optical head 23,so that a recording mark is formed. It is understood that although theapparatus is disclosed schematically, it includes elements such as anautomatic focusing (AF) means and tracking means as part of thetransducing system generally referred to as the optical head 23.

[0039] At the time of playback on the other hand, the intensity changeof the laser beam reflected from a target address on the disk 24 isreceived by a light detector 25 in which the laser beam is convertedinto an electrical signal. Then the electrical signal is input via areproduced signal amplifier 26 to a waveform equalizer 27. Then, thebinary signal is formed by a discriminator 28 and decoded by a decoder29 into a data bit string (information). Next, a preformatted area(header) of a target address is detected and analyzed by header reader33. Then, the dummy signal and header are deleted by dummy signal andheader deleter 34, and a reproduced user data signal 35 is obtained.

[0040] Next, it is determined if the reproduced signal representscontrol data by a control-data detector 36. If the reproduced signalcontains control data including information on the dummy data pattern,the dummy data information is picked up from the control data by dummydata information separator 39. Then, the dummy signal is generatedaccording to the information (dummy data) on the dummy data pattern bydummy data pattern generator 40. If the reproduced signal is not controldata, the data is stored in memory 38 through reproduced user datacontroller 37.

[0041] As a modification of the embodiment disclosed with respect toFIG. 3, a bit array (data area postamble) can be added by postambleadding circuit 43 before the dummy data recorded in the dummy area 16,and the inversion of the ratio of the recording mark and the space forthe dummy signal can be avoided. The postamble pattern is generated inaccordance with the user data to be recorded and is added to the userdata by adder 43 at the position just after the user data in thedirection of recording.

[0042]FIG. 4 shows a flow chart of the steps followed when a disk isinserted in the record playback apparatus of the present invention.First, in step 45, it is detected that the disk is set in the drive byan optical or mechanical sensor. Then, the optical head is moved to, forexample, the innermost area of the disk in step 46 and readinginformation starts in step 47. In step 48, the reproduced signal is readout and amplified from the rotating disk, and then the wave formgenerated thereby is equalized, digitized and decoded in steps 49-51,respectively. The control data is extracted by deleting thesynchronizing signal, etc. in step 52 and in step 53 the information ofthe dummy data pattern is taken from the control data. Such information(dummy data) includes, for example, the specification of the duty ratioof the dummy signal to be recorded being added to the user data. In step54, the dummy data pattern is generated and stored in step 55 in amemory so that the dummy signal can be added when user data is to berecorded.

[0043] An example of the data area postamble is shown in FIG. 5 as 31and the dummy data as 32. Patterns (a) and (b) show the case where theend of the user data is a binary “0”, and patterns (c) and (d) show thecase where the end of the user data is a binary “1”. Accordingly,patterns (a) and (c) show the case where the end of the user data is amark. Patterns (b) and (d) show the case where the end of the user datais a space. It is preferable if the postamble is provided according tothe known signal modulation standard.

[0044] An example of recording the information on the dummy data patternin the control data area is shown in FIG. 6(a). The dummy signal area isdivided into two sub areas, and the dummy signal pattern informationarea in the control data area is also divided into two sub areas; eachsub area being divided into three sections. A mark length, expressed inunits of Tw, is recorded using 4 bits in the first section. A spacelength, which is expressed in units of Tw, is recorded using 4 bits inthe second section. The number of repetitions of these marks and spacesis recorded using the following 8 bits (1 byte). Then, a mark length, aspace length, and the number of repetitions in the second sub area isrecorded using 16 bits. Thus, the whole pattern of the dummy dataexpressed by marks and spaces is represented by 4 bytes of control data.

[0045] In other examples, a single repetition pattern of a mark and aspace can be written in the dummy data pattern information area, or 3patterns can be written dividing the dummy data area into 3 sub areas.When the dummy data area is divided into more than 4 areas, the requiredspace to represent the patterns in the control data area exceeds 4bytes.

[0046] As another example, the basic mark and space arrangement, whichis repeated in the first sub area of two sub areas in the dummy dataarea, is recorded in the control data area using 2 bytes in the samemanner as in the dummy data area, and the basic mark and spacearrangement in the second sub area is recorded using the following 2bytes as shown in FIG. 6(b). In this method, 4 bytes are used in thecontrol data area to represent the pattern in the dummy data when thenumber of sub areas is two, and more than 4 bytes are used when thenumber of sub areas are more than 3 just like the former example.

[0047] Although a description has been given of the continuous servosystem by way of example, the same effect is achievable with a sampledservo system in a like manner as set forth herein. Further, although alaser beam has been disclosed for recording, it is possible to use anelectron beam or an ion beam instead of the laser beam in accordancewith the present invention.

We claim:
 1. An information recording medium on which information isrecorded in a recording area by means of energy beam irradiation,comprising: a pattern of a dummy signal added to at least one of theleading and trailing sides of the recording signal which is recorded inthe recording area.
 2. An information recording medium as claimed inclaim 1, wherein a postamble is added between user data and the trailingside dummy signal.
 3. An information recording medium as claimed inclaim 1, wherein said recording medium has a phase change recordingfilm.
 4. An information recording medium as claimed in claim 3, whereinsaid recording film is one of a Ge—Sb—Te system and a Ag—In—Sb—Tesystem.
 5. An information recording medium as claimed in claim 4,wherein said recording film contains a high-melting point materialselected from one of Cr—Te and Ag—Te.
 6. An information recording mediumas claimed in claim 1, wherein, in order, a protective layer, arecording layer, a protective layer, a first reflective layer and asecond reflective layer are stacked on a substrate.
 7. An informationrecording medium as claimed in claim 1, wherein information concerningthe pattern of the dummy signal is recorded in a control data area onthe recording medium.
 8. An information recording medium as claimed inclaim 7, wherein an information on a pattern of the dummy signal inwhich the average recording mark length is shorter than the averagespace length between recording marks is written in the control dataarea.
 9. An information recording medium as claimed in claim 7, whereinan information on the pattern of a single-frequency dummy signal iswritten in a control data area.
 10. An information recording medium onwhich information is recorded in a recording area by means of energybeam irradiation, comprising: a dummy area in which information to berecorded by a dummy signal is added to at least one of the leading andtrailing sides in the recording area in which an information signal isrecorded on the recording medium.
 11. An information recording method inwhich information is recorded on a recording medium by means of energybeam irradiation, comprising recording with an energy beam a dummysignal added to at least one of the leading and trailing sides in therecording signal.
 12. An information recording method as claimed inclaim 11, further comprising using a laser for said recording of saiddummy signal, wherein an average energy of the laser beam during dummysignal recording is lower than an average energy used to record userdata signal.
 13. An information recording method as claimed in claim 11,further comprising using a laser for said recording of said dummysignal, wherein in said recording, the dummy signal is recorded with asingle-frequency and wherein the average energy of the laser beam forsaid recording of said dummy signal is set lower than an average energyused to record user data signal by adjusting the duty ratio of the dummysignal.
 14. An information recording method as claimed in claim 13,wherein the average energy of the laser beam during dummy signalrecording is decreased stepwise or linearly by adjusting the duty ratioof the dummy signal stepwise or linearly.
 15. An information recordingmethod as claimed in claim 11, wherein a position where the recording ofthe signal including the dummy signal starts is shifted at random. 16.An information recording method as claimed in claim 15, wherein themaximum shift width of the recording start position is shorter than thelength of the dummy signal.
 17. An information recording method asclaimed in claim 16, wherein the maximum shift width of the recordingstart position is in a range of about {fraction (1/20)}-½ of the lengthof the dummy signal.
 18. An information recording apparatus forrecording information by means of energy beam irradiation, comprising: alaser beam source, an optical system, automatic focusing (AF) means,tracking means, a recording medium on which information is recorded insingle or plurality of recording area by means of the laser beam, meansfor rotating the recording medium, means for condensing the laser beamfrom the laser beam source on the recording medium, signal modulatingmeans for converting a signal to be recorded into a modulation code,means for adding a dummy signal or dummy signals to at least one ofleading and trailing sides in the recording signal, recording waveformgeneration means for generating a recording waveform corresponding to arecording signal, recording start position control means for shifting arecording start position at random, laser driving means for driving thelaser beam source in accordance with the recording waveform, means forconverting the intensity change of the laser beam reflected from therecording medium into an electrical signal, means for amplifying thereproduced electrical signal, conversion-to-binary means for convertingthe electrical signal into a binary waveform, means for decoding thebinary signal to make the decoded signal, means for reading apreformatted header signal, means for deleting the dummy signal, meansfor finding control data from said decoded signal, means for pick upuser data from the decoded signal, means for extracting information onthe dummy data pattern, means for generating dummy data, and means forstoring the dummy data pattern.